The proposed studies will use the digastric muscle of the rabbit, a simple model of an oral striated muscle, to develop an isometric length-tension sarcomere diagram. The digastric muscle tendon can be attached directly to an apparatus for measuring and recording active and passive muscle tension and muscle length. Sarcomere lengths will be measured from the digastric muscle, fixed at the end of the length-tension experiment by arterial perfusion of 10% formalin. Muscle fiber length and cross-sectional area will also be measured for use in constructing the isometric length-tension sarcomere diagram. The completed isometric length-tension sarcomere diagram will then be used to estimate force production capability of the intact digastric muscle. Additional animals will be sacrificed by fixing the head with the jaws in various functional positions. Muscle length and sarcomere length will be measured at these known jaw positions and compared to the independently determined values for muscle length and force production of the length-tension sarcomere diagram. These experiments should yield information about the range of muscle lengths and sarcomere lengths for the functional jaw positions and should also provide a good estimate of muscle force capability throughout the functional range.